Communication system



Nov. 20. .1928. 1,692,118

M. P. HANSON COMMUNICATION SYSTEM Filed May 10, 1927 Patented Nov. 20, 1928.

UNITED STATES 1,692,118 PATENT OFFICE.

MALCOLM P. HANSON, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIRED RADIO, INC., OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

COMMUNICATION SYSTEM.

Application filed Kay 10, 1927. Serial No. 190,223. I

My invention relates broadly to communication systems and more particularlyto a compact arrangement of comblned signal transmission and reception apparatus.

5 One of the objects of my invention is to provide a combined continuous wave signal transmission and reception apparatus wherein the keying circuit is arranged to render the receiving apparatus effective interme- 1n diatethe transmission periods.

Another object of my invention is to provide a signal transmission receiving apparatus in which the electron tube oscillator at the transmitter may be utilized as the local 1 generator of oscillations for a heterodyne receiver, the conditions of the oscillator being modified by the actuation of the keying circuit for rendering the oscillator eflective by the receiver intermediate the signaling pc- 0 riods.

My invention will be more clearly understood by reference to the following specificatlon and the accompanying drawings, in which: 1

Figure 1 illustrates a combined transmission and receiving system employing the principles of my invention, and Fig. 2 represents a modified form of circuit arrangement employed for the oscillator which is alternately used for transmission and receiving purposes under control of the keying circuit.

In inter-communication between small single tube, piezo electric crystal controlled transmitters, the crystal controlled oscillating tube is difficult to key if tube oscillations cease entirely when the key is up. It is possible and desirable to provide for residual weak oscillations when the key is up, so that oscillations will build up to full strength rapidly and dependably when the key is depressed. Such residual oscillations in the past have been objectionable by their preventing the use of the break-in method for two-Way communication on the same freuency, as they have caused so much interference in an adjacent receiver as to blanket reception of a distant signal of same frequency. Y

My invention makes use of this otherwise objectionable residual oscillation by rendering it suitable as' a heterodyne oscillation source for beat note reception, and employs the transmitting crystal to provide crystal controlled reception with freedom from vibration effects and calibration uncertainties,

and enables reception of strong signals without blocking. It accomplishes these things in the following manner:

(a) It provides the necessary slight frequency shift of the residually sustained oscillations sufficient to cause heterodyne reception at the desired audible beat note of signals being received on the common transmitting frequency.

(6) It provides means for reducing the intensity of oscillations in the transmitting circuit to any desired residual value suitable for heterodyne function.

(c) It eliminates, when the circuit is in residual oscillations, modulation du to any voltage irregularity or ripple peculigr to the plate power source, which may not be objectionable in transmission, but which would interfere with proper heterodyne function.

(d) It provides a suitable adjustable degree of electrical coupling between the receiver and the transmitting circuit while the latter is in residual oscillation and acting as a heterodyne source.

(e) It changes the transmitting circuit from the emitting to the heterodyning condition quickly, thus enabling rapid break-in communication, with a ke ing contact sequence such as to reduce t e possibility of accidental damage to the receiver or any part pf the transmitter circuit in normal opera- It should be noted that the maximum controllable frequency variation of a crystal controlled oscillation circuit, attainable by methods herein described, appears to be a fraction of one per cent, sufficient for satisfactory heterodyne detuning at high communication frequencies.

The circuit arrangement of my invention will be understood by reference to Fig. 1 of the drawings which represents one form of transmitting circuit embodying the princi- 'ples of my invention. The diagram shows a form of crystal controlled transmitting circuit together with suitable connections to receiver R which may be of any conventional type, but should not be in self-oscillating condition. All keying contactsin the trans mitting circuit are shown in the position for reception allowing only residual oscillation. The oscillating tube 1 derives its filament current from a source 2 and its late voltage from a source 3, shunted by a y-pass condenser 4 if necessary to reduce any voltage fluctuations.

Residual oscillations of desired strength are maintained by reducing "the effective plate voltage through resistor 5; audio frequency modulation due'to any.

voltage ripple is prevented bya suitable fil-' ,ter system such as audio frequency choke coil 6and by-pass condensers 7 and 8. This choke coil 6 may be of high resistance up to a value where it gives sufficient voltage drop in itself so as to dispense with a separate resistor 5. I I

The oscillation frequency of the circuit is governed by quartz crystal 9; the radio frequency milliammeter 10 indicates the relative strain on the crystal during transmission and hus insures pro-per circuit adjustment. The variable inductance coil 11 shunted if desired by variable condenser 12 in the residually oscillating condition provides the slight frequency change desirable for a proper heterodyne note and permits to some extent compensation for a relative frequency change of the incoming signals resulting from tempera 'ture changes, etc., at the local or the distant station, The plate circuit of tube 1 connects to oscillation transformer 14; which is properly tuned by variable condenser 15. During transmission, 14 is coupled to the antenna 16 and ground 17 either conductively as shown, or by other suitable means. For receiving purposes the residual oscillation frequency of the circuit is superimposed in a suitable degree and manner upon the incoming signals received on the antenna. This may be effected in a simple manner by the inherent capacity coupling across the open transmit- 1 ting contact of key 18 and suitable adjustment of the intensity of residual oscillation by resistor 5. I have found of advantage the use of a slight additional variable inductive cou-' plin through coil 19 which may be so rotate thatit either suitably reinforces the residual coupling at 18 or by phaseopposition reduces it to the desired value, the best coupling value depending upon strength of the incoming signals and other variable conditions.

. Telegraphic keying is effected by a multiple contactor switch system 20 having mechanically connected contact arms 21, 22 and 18. This device may be directly hand operated or may be operated by a relay through electro-- magnet 42 and hand key 23 as shown. Contact 21 short circuits the detuning circuit rendering it ineffective when in the transmitting position. Contact 22 applies full plate voltage to the oscillator tube 1 byshort circuiting l the voltage-reducing resistor 5 and the filter Y inductance 6 when 1n the transmittmg pos tion. '18 switches the common antenna 16 from the receiver R to the transmitter. It is desirable, for the protection of the circuit that when the key is closed, contact 22 should close after contacts 21 and 18 and, inversely,-

be the first one toopen as the key is released.

above mentioned circuits.

This is accomplished by proper adjustment of the spring contacts and clearances by means of the screw means shown at 24, 25 and 26. Fig. 1 shows adjustmentfor a closing sequency 21, 18, 22 and an opening sequency in reverse order. Thus the detuning is made inefiective by 21 before application of fulltransmitting voltage through 22 and remains so until the plate voltage has again been reduced to residual oscillation value by opening of T5 22; this prevents injurious overloading of the quartz crystal 9 due to any regeneration inherent in the detuning method. The connection of the antenna 16 to the transmitter through contact 18, before 22 applies full voltage and inversely the opening of 18 subsequent to that of 22 likewise prevents'possible damage to the crystal 1 from momentary oscillation at full power without the outpiit load. 21 and 18 may make simultaneous contact for transmission, but in view of the de sirable clearance of contact due to the radio frequency voltage involved, 18 can be adjusted to make transmitting contact after 21 as shown or its lever arm may be lengthened to provide greater travel.

The variation of oscillation frequency of the crystal controlled circuit, for purposes of my diagram by means of detuning inductance 11 and optional condenser 12, may be accomplished .in a variety of ways which may (6) Variation of the plate circuit reactance by changing 14,15 or 29.

(0) By introducmga -var1able degree of electrostatic or electromagnetic coupling between the crystal, or grid and plate circuit of the tube 1. e I

(d) By changing the effective reactance of a secondary circuit coupled to either the grid circuit or plate circuit or both.

(e) -By resistance variation in any of the Fig. 2, shows'a modification of the plate supply circuit of Fig. 1, whichemploys a battery 30 or well filtered, separate source of reduced plate voltage for residual oscillations and heterodyne purposes. This arrangement 11a is particularly adapted to cases where a transmltting plate supply source 3 is employed having highinherent or intentional modulation such as rectified .A. 0., that would be unsuitable for a heterodyne power source 1% without use. of an expensive filter system, or

where the voltage delivered by source 3 fluc- .tuates. Relay arm 22 through a back contact 22 connects the plate of tube 1 to this battery during heterodyne reception, and '125 switches therefrom to the high voltage source, 3 while-=the-key is depressed during trans mission. Condenser 31 is used to store up sufficient ener to serve as'power source to maintain oscilations during the transfer II M period of 22 and in connection with resistance 32 absorbs the initial voltage surges during transmission. Condenser 33 and resistor 34 reduce sparking at the transmit-ting contact of 2-2. A connection through suitable resistor 35 may be employed, if desired, for the purpose of maintaining thecharge of battery 30 by momentary charging during transmission.

While the principles of my invention have been described only in their application to a single tube transmitter, they are also applicable to larger sets employing a crystalcontrolled oscillator with one or more stages of output amplification. While in such transmitters balancing methods are generally employed to prevent or neutralize direct coupling between successive circuits, it is usually impossible to completely shield or neutralize the master oscillator from an adjacent receiver to prevent interference with reception on the same frequency. By applying my method of detuning to the master oscillator and suitable coupling its oscillations to the receiver when the key is up, intercommunication on the same frequency is facilitated.

' The special advantages gained by my sys tem as herein described are:

(a) It permits int-ercommunication by the break-in method with undamped waves between crystal controlled transmitters, with receivers in close proximity, all operating at tile same frequency or in harmonic relations 1p.

(6) It provides the advantages of crystal controlled transmission and reception without requiring the use of separate crystals for reception purposes.

(0) It provides selection of optimum receiving conditions by variation of strength of the heterodyne by adjusting the intensity of the residual oscillation of the transmitter or by variable coupling of the receiver thereto.

(d) Beat note reception of relatively high powered continuous wave signals at close range is made possible without blocking of the receiver, since a crystal controlled and relatively powerful heterodyne source is used.

The signal transmission and receiving apparatus of my invention has been found to be extremely practical in operation and while I have described the invention in connection with a short'distant communication system, it will be understood that embodiment of my invention disclosed herein is merely illustrative of my invention and that modifications in the circuit arrangementof the communication system may be made without departing from the spirit of my invention within the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A signal transmission and receiving system comprising an antenna ground circuit, radio receiving apparatus, radio transmission apparatus including an electron tube oscillator and a piezo electric crystal control circuit connected with said electron tube oscillator, a switchin system comprising a plurality of sections, eying means for controlling the operation of said switching system, one section of said switching system being arranged to detune said piezo electric crystal control circuit, another sectionrof said switching system being arranged to modify the amplitude of oscillations sustained by said oscillator, and another section of said switching system being arranged to control the connections between said antenna ground circuit, said radio receiving apparatus and said radio transmission apparatus.

2. A signal transmission and receiving system comprising an antenna ground circuit, signal receiving apparatus, signal transmission apparatus, switching means for alternately establishing connection between said antenna ground circuit and said signal receiving and transmission apparatus, said transmission apparatusinclu'ding an electron tube oscillator, a piezo electric crystal system capable of generating oscillations sustained by said piezo electric crystal system, and separate switching means simultaneously operative with the actuation of said first mentioned switching means for detuning said piezo electriccrystal s stem and modifying the amplitude of oscil ations developed by said electron tube oscillator in accordance'with telegraphic signals.

3. In a signal transmission and receiving system an antenna ground circuit, a continuous wave signal receivin apparatus, signal transmission apparatus including an electron tube oscillator, a piezo electric crystal control circuit connected with said electron tube oscillator whereby oscillations of a frequency determined by said piezo electric crystal control circuit may be sustained by said electron tube oscillator, said receiving apparatus being selectively tuned to a frequency remote from the frequency of said electron tube oscillator, and switching means including a plurality of separate sections, one section of said switching means being arranged to effect a detuning of said piezo electric crystal control circuit, another section of said switching means being arranged to modify the amplitude of the oscillations sustained by said electron tube oscillator, and -another section of said switching means being arranged to transfer connections from said antenna ground circuit to said signal receiving apparatus and to said signal transmission apparatus, said electron tube oscillator bein adjusted to sustain oscillations controlled piezo electric crystal control circuit for imy the detuned condition of said vthe incoming signaling frequency.

reception an antenna ground cir- 4. A signal transmission and system comprlsin cuit, a signal recelving circuit, a radio transi mitter including a piezo electric crystal control circuit andan electron tube oscillator for sustaining oscillations at the frequency of said piezo electric crystal control circuit, a coupling between said electron tube oscillator and said signal receiving circuit, switching means constituted b a plurality of independent sections, a eying circuit for simultaneously controlling the movement of said independent sections, the first of said sections being arranged to effect a detuning of said piezo electric crystal control circuit, the second of said sections beingv arranged to effect a modification of the amplitude of the oscillations developed by said electron tube oscillator, and a third section'being arranged to transfer connections from said antenna ground circuit to said radio transmitter or receiving circuit, said second mentioned section operating to restore the amplitude of the oscillations of said electron tube oscillator to a normal conditionsubsequent to the closing of said first and third mentioned switching sections.

5. A transmission and receiving system comprising a continuous wave receiving apparatus, an antenna ground circuit, a signal transmission. apparatus including a piezo electric or stal control circuit, an electron tube oscillator and a pair of independent output circuits, switching means for transferring connections between said antenna ground circuit and said signal transmission and receiving system, and means simultaneously actuated in accordance with the oper-- ation of said switching means forrendering one of said output circuits inefiective for changing the operating condition of said electron tube oscillator for efiectively impressing local oscillations u on said receiving apparatus intermediate t e signal transmission periods.

MALCOLM P. HANSON; 

